| Agricultural machinery automation is the key direction of agricultural development in our country.Autonomous walking of farm machinery has always been the focus of research.In order to realize the autonomous walking of agricultural machinery,it is necessary to locate it,and positioning is the premise of autonomous walking.The location of agricultural machinery must be high precision and low price.Taking rice as an example,the spacing between plants is between 200-250 mm,which sets high requirements for the positioning of agricultural machinery.And the field crops are relatively small,the visual way is difficult to identify.In this paper,on the basis of DGPS and visual positioning,in view of farmland operation and considering the adaptability of field operation,a positioning device based on flexible cable distance measurement is proposed.This device can be carried out in field operation and the target precision reaches 20 mm.The research work in this paper mainly includes the following aspects:(1)The research and design of the cable length measurement device.On the basis of the flexible cable distance measuring principle,the long flexible cable measuring mechanism is studied and designed.The maximum measurement error is20 mm,the response frequency is 600 Hz,and the maximum loss rate of the encoder pulse is 0.0025%.The nanowire mechanism has been researched and designed,so that the length of the flexible cable can reach 150 meters,so that the device can adapt to the field farm machinery.(2)Research and design of the buffer mechanism based on laser range finder.The swing of agricultural machinery when walking in the field is easy to cause the cable fracture.In this paper,a relaxation buffer mechanism is designed and studied,which can accommodate the expansion displacement buffer in the 40-200 mm range.In the buffer mechanism,the laser side distance sensor is used to measure the expansion displacement of the buffer mechanism,and four sets of data are measured every 50 mm in the length of the 50mm-200 mm range,respectively.The results show that the average length of 50 mm is 53.95 mm,the maximum error is5 mm,and the average relative error 7.9%;The average length of 206.51 mm is200mm,the maximum error is 10 mm,and the average relative error is 3.23%.The method of Calman filter is used to filter the measured data,which improves the stability of the data and reduces the random error.The error is controlled within 3%after the Calman data filtering.(3)The serial communication and I2 C communication of Raspberry Pi and Arduino are studied.The principle of two communication modes and the implementation methods on Raspberry Pi and Arduino are analyzed.I2 C communication is realized on Raspberry Pi and Arduino,and the baud rate of I2 C communication is 32 KHz.The length measuring mechanism and buffer mechanism were integrated to locate the location on Raspberry Pi.The result shows that the positioning error is less than 20 mm.(4)Research and experiment of mixed location method.In order to study and test the location of this paper,a car was designed,and the driving and control principle of the car was analyzed.The friction transmission mechanism is designed on the car wheel,and the pulse of the encoder is transformed into the distance of the trolley.In order to locate the trolley and mix the location mode of the cable distance,the integrated positioning of the farm machinery is carried out.The maximum error within 1 meters is 20 mm.Cumulative error has increased rapidly.This hybrid positioning method provides a way for the future hybrid positioning of unilateral measurements. |
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